Conduit coupling assembly

ABSTRACT

A coupling system for conduit and pipe for carrying insulated electrical cable, more particularly, a conduit coupling assembly for connecting multiple lengths of conduit in coaxial relationship.

FIELD OF THE INVENTION

The present invention relates to a coupling system for conduit and pipethat contain electrical cable or wiring, more particularly, a conduitcoupling assembly for connecting multiple lengths of electrical conduitin coaxial relationship, particularly for carrying insulated electricalcable.

BACKGROUND OF THE INVENTION

The present invention relates to a conduit coupling assembly forconnecting multiple lengths of conduit in coaxial or end-to-endrelationship. It is a conventional practice in many types of pipe orconduit systems, and particularly in electrical systems employingtubular conduits that contain electrical wires or cables, to connect anumber of lengths of conduit in end-to-end relation through means ofcouplings so as to form a continuous conduit system as necessary for aparticular application. In the case of thin wall conduit, which isprimarily employed for encasing electrical cable or conductor wires inapplications where the conduit will not be subjected to large stresses,compression fittings or coupling assemblies may be employed which areswaged or otherwise affixed to adjacent ends of conduit lengths. Theconduit is generally available in different lengths and may be quitereadily formed to various bend contours and coupled end-to-end throughthe compression couplings or coupling assemblies.

One known technique for connecting lengths of conduit in coaxial orend-to-end relationship is to provide external threads of standard sizeon the opposite ends of each length of conduit and then connect thelengths of conduit through coupling assemblies. Those couplingassemblies have internal threads, which enable threaded connection withadjacent ends of the conduit lengths to form a structurally sound andelectrically sound connection. One known coupling assembly for couplinglengths of conduit is disclosed in commonly assigned U.S. Pat. No.4,957,314 to Basile et al.

The coupling assembly disclosed in the Basile et al. patent requiresspecially manufactured components, including outer and inner couplingassemblies that must be first installed on each length of conduit beforethe lengths of conduit can be coupled together. More specifically, thecoupling assembly utilizes outer and inner coupling members havingthreaded ends for threading onto the ends of the lengths of conduit. Theouter coupling member is threaded or screwed on to one end of one lengthof conduit and the inner coupling member is threaded or screwed onto oneend of the other length of conduit. The lengths of conduits are thenaxially aligned and the inner coupling member is inserted into the outercoupling member. The inner coupling member is firmly held in the outercoupling member by set screws disposed on the outer coupling member.

Other known coupling assemblies are disclosed in commonly assigned U.S.Pat. No. 4,547,004 to Goldberg and U.S. Pat. No. 4,592,574 to Vollmuthet al. Similar to the coupling assembly disclosed in the Basile et al.patent, the coupling assemblies disclosed in the Goldberg and Vollmuthet al. patents require specially manufactured components, includingouter and inner coupling members that must be first installed on onelength of conduit before the lengths of conduit can be coupled together.Those outer and inner coupling members have threaded ends and thelengths of conduit are subsequently joined by rotating the outercoupling member to thread or screw it onto the other end length ofconduit.

Another known technique for connecting lengths of conduit is to providelengths of conduit with built in set screw assemblies. Morespecifically, each length of conduit includes a receiving end having anenlarged bell portion or increased diameter that is shaped andconfigured to receive the insertion end of another length of conduit. Inaddition, set screws are disposed in apertures located on the bellportion and are used to mechanically hold the insertion end in the bellportion. During installation, the insertion end is positioned in thebell portion and the set screws in the bell portion are advanced ortightened until it engages the insertion end to firmly hold theinsertion end in the bell portion. Such a coupling assembly has manyadvantages over other known techniques for connecting lengths ofconduit. For example, such a coupling assembly eliminates the need formultiple components, such as outer and inner coupling members. Thus, theincreased cost and time associated with the inventory, shipping, andfactory and field installation of the multiple components is eliminated.

Even though those built in set screw coupling assemblies have manyadvantages over other known techniques for connecting lengths ofconduit, improvements in those set screw coupling assemblies are needed.For example, a need exists for a built in set screw coupling assemblythat (1) reduces the amount of time needed to tighten the screws orbolts during the conduit installation process, (2) reduces or eliminatesthe amount of offset typically caused when several conduits areassembled and joined together, (3) reduces or eliminates the amount ofdimpling or denting that may occur on the insertion end of the length ofconduit when the set screws are tightened, (4) reduces or eliminates thepossibility that a set screw will vibrate loose from the tightenedposition, (5) increases the mechanical connection between the lengths ofconduit, and (6) increases the safety of the conduit system byeliminating or reducing any damage of the electrical cable at theconnection joint between the length of conduit. Those improvements,among others, are found in the present invention.

BRIEF SUMMARY OF THE INVENTION

Briefly, the present invention is a coupling system for connectingmultiple lengths of conduit in coaxial or end-to-end relationship. Eachlength of conduit includes an insertion end and, at the other end, abell portion that is shaped and configured to receive the insertion endof another length of conduit. To assemble the lengths of conduit incoaxial relationship, the insertion end of one length of conduit isinserted or positioned into the bell portion of another length ofconduit. To provide an improved mechanical connection between theinsertion end and the bell portion, the difference between the innerdiameter of the bell portion and the outer diameter of the insertion endis less than 0.060 inches and the nominal length of the bell portion isat least 3 inches. Reducing the difference between the inner diameterand the outer diameter results in reduced gap or space between theinsertion end and the bell portion when the insertion end is positionedin the bell portion. In turn, the reduced gap or distance substantiallyreduces or eliminates the amount of offset typically caused when severalconduits are assembled and joined together. Thus, several conduitsjoined together will define a relatively straight line.

To secure the length of conduit together, the bell portion of eachlength of conduit contains a built in set screw or bolt assembly. Thebell portion contains threaded rivets for receiving set screws. Thethreaded rivets are disposed in apertures positioned on the bellportion. Once the insertion end is inserted into the bell portion, thelengths of conduit are secured together by tightening the set screwsuntil the bottom of the set screws contacts the insertion end. The setscrews contain thread profiles that measure between 4 and 12 threads perinch and lengths between about 0.5625 and 0.450 inches. Because thepresent invention incorporates this improved set screw design, onlyabout a ¼ to 1½ turn of the set screw is needed to adequately tightenthe set screw. In addition, as a result of the improved set screwdesign, the head of the set screw fits firmly and securely on the rivetand the contacting surface of the set screw fits firmly and securely onthe outer surface of the insertion end of the conduit when the requiredamount of torque to adequately tighten the set screw is reached.Moreover, the improved design enables an operator to quickly andefficiently tighten the screw against the outer surface of the insertionend of the conduit. In addition, the improved design eliminates theguesswork in determining whether the set screw is in the locked ortightened position and in determining whether enough torque has beenapplied to adequately tighten the set screw. Furthermore, the improveddesign substantially reduces or eliminates the possibility of anydimpling or denting that may occur on the insertion end caused by overtightening the set screw and substantially reduces or eliminates thepossibility that the set screw will vibrate loose from the tightenedposition.

These and other important features of the present invention may best beunderstood with reference to the accompanying drawings and in thefollowing detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing aspects and many of the advantages of the presentinvention will become readily appreciated by reference to the followingdetailed description of the preferred embodiment, when taken inconjunction with the accompanying drawings, wherein:

FIG. 1 depicts two lengths of conduit in coaxial relationship whereinthe insertion end of one length of conduit is positioned in thereceiving end of another length of conduit;

FIG. 2 depicts a cross-sectional view of the receiving end of one lengthof conduit;

FIG. 3 is a cross-sectional view depicting the insertion end of onelength of conduit positioned in and mechanically coupled to thereceiving end of another length of conduit;

FIG. 4 an enlarged bottom view depicting the inside surface of therivets and the contacting surface of the set screws utilized in thepresent invention; and

FIG. 5A depicts an end expander prior to insertion in the length ofconduit;

FIG. 5B depicts an end expander inserted in a length of conduit forminga bell portion;

FIG. 6 is a schematic of an exemplary embodiment of the multi-taskstation used to manufacture the length of conduit; and

FIG. 7 is a schematic of another exemplary embodiment of the multi-taskstation used to manufacture the length of conduit.

DETAILED DESCRIPTION OF THE INVENTION

For a better understanding of the present invention, reference may behad to the following detailed description taken in conjunction with theaccompanying drawings. FIG. 1 depicts a coupling assembly 10 forconnecting a pair of lengths of conduit 12, 14 in coaxial relationship.The lengths of conduit 12, 14 are preferably of the same outer diameterand have insertion ends 16 and receiving ends 18. Each receiving end 18is defined by a bell portion 20. Referring to FIG. 2, the diameter ofthe insertion end 16 transitions into the diameter of the bell portion20 at a transition run 22.

As shown in FIG. 3, the bell portion 20 has an inner diameter slightlylarger than the outer diameter of the insertion end 16, and the bellportion 20 is shaped and sized to receive the insertion end 16 duringassembly of the lengths of conduit 12, 14. The transition run 22 servesas an abutment for limiting the extent that the insertion end 16 can beinserted into the bell portion 20. Preferably, the insertion end 16 andthe bell portion 20 are sized such that when the insertion end 16 isinserted into the bell portion 20, the gap or distance between an outersurface 24 of the insertion end 16 and an inner surface 26 of the bellportion 20 is minimized or reduced. To minimize that gap or distancebetween the outer surface 24 and the inner surface 26, the difference ortolerance between the inner diameter of the bell portion 20 and theouter diameter of the insertion end 16 should be less than 0.060 inches.More preferably, the distance between the two diameters is about 0.025inches. The reduced gap or distance between the outer surface 24 of theinsertion end 16 and the inner surface 26 of the bell portion 20provides for an improved mechanical fit between the two lengths ofconduit 12, 14. Moreover, the reduced gap or distance reduces oreliminates the dimpling that may occur on the insertion end 16 when thelengths of conduit 12, 14 are coupled (as explained in detail below). Inaddition, the reduced gap or distance provides better overall geometrythat reduces the amount of time needed to tighten the screws or boltsduring the conduit assembly process (as explained in detail below).Furthermore, the reduced gap or distance between the outer surface 24 ofthe insertion end 16 and the inner surface 26 of the bell portion 20reduces or eliminates the amount of offset typically caused when severalconduits are assembled and joined together. As a result, the severalconduits joined together will be substantially aligned in co-axialrelationship and the central axes of the several conduits will define arelatively straight line.

Referring back to FIG. 2, the bell portion 20 has at least one aperture30 formed therethrough. If the bell portion 20 has more than oneaperture 30, the apertures 30 may be radially and/or longitudinallyaligned on the bell portion 20. In the preferred embodiment, the bellportion 20 has two regularly spaced apertures 30 which arelongitudinally aligned on the bell portion 20. Rivets 32 are fixedlysecured within the apertures 30. Each aperture 30 may be located on araised boss or crest 34 so that when the rivets 32 are disposed orseated within the apertures 30, the inside surface 36 of the rivets 32sit substantially flush with the inner surface 26 of the bell portion 20(depending on the gap existing between the outer surface 24 of theinsertion end 16 and the inner surface 26 of the bell portion 20). Eachrivet 32 is threaded to receive a set screw 38. The set screws 38 may beof the type which can be advanced using an Allen wrench or may have anyother suitable extending head for engagement by a suitable wrench,screwdriver, or the like. As shown in FIG. 4, the inside surface 36A ofthe rivets 32 and/or a contacting surface 40A of the sets screw(s) 38may contain a serrated pattern or other suitable pattern to providefrictional engagement between the rivets 32 and/or the set screw(s) 38with the outer surface 24 (not shown) of the insertion end 16. Inaddition, the outside surface of the rivets 32 and the underside surfaceof the head of the set screw(s) 38 may also contain a serrated patternor other suitable pattern to provide enhanced frictional engagementbetween the outside surface of the rivets 32 and the underside surfaceof the head of the set screws 38. Such a construction provides apositive locking between the rivets 32 and the set screws 38 when theset screws 32 are in a tightened position and further avoids the setscrews 38 from vibrating loose from that tightened position duringvibration of the interconnected lengths of conduits 12, 14.

During assembly of multiple lengths of conduit 12, 14, as shown in FIG.3, the insertion end 16 is positioned into the bell portion 20 until theinsertion end 16 abuts the transition run 22. The set screws 38 are thentightened to mechanically couple the lengths of conduit 12, 14 together.The apertures 30 containing the set screws 38 should be located asufficient distance from the transition run 22 and the edge 23 of thelength of conduit so that when the set screws 38 are tightened, anydimpling that may occur on the insertion end 16 will be reduced oreliminated. Preferably, the center of the apertures 30 containing theset screws 28 are located at least 0.8125 inches from the end 39 of thetransition run 22, preferably between about 1.3125 and 1.8125 inchesfrom the transition run 22. In addition, center of the aperturescontaining the set screws 28 are located at least 0.8125 inches from theedge 23 of the length of conduit.

Preferably, each set screw 38 is a 5/16 set screw with a double ortriple lead thread, or any suitable broad thread design. In addition,the set screw 38 preferably contains a thread profile 41 that measuresbetween 4 and 12 threads per inch and a length 42 between about 0.5625and 0.450 inches, preferably 0.450 inches. The thread profile 41 and thelength 42 of each set screw 38 should be dimensioned such that onlyabout a ¼ to 1½ turn of the set screw 38 is needed to adequately tightenthe set screw 38.In addition, the length 42 should be sized so that whenthe required amount of torque to adequately tighten the set screw 38 isreached, the head of the set screw 38 fits firmly and securely on therivet 32 and the contacting surface 40 of the set screw 38 fits firmlyand securely on the outer surface 24 of the insertion rod 16.Accordingly, only about ¼ to 1½ turn of the set screw 38 is neededbefore the set screw 38 fits firmly and securely on the outer surface 24of the insertion rod 16. Preferably, the torque required to adequatelytighten the set screw 38 is between about 50 to 130 in-lb. Such aconstruction enables an operator to quickly and efficiently tighten thescrew 38 against the outer surface 24. Moreover, such a constructionsubstantially eliminates the guesswork in determining whether the setscrew 38 is in the locked or tightened position and in determiningwhether enough torque has been applied to adequately tighten the setscrew 38. Furthemore, such a construction reduces or eliminates thepossibility that any dimpling may occur on the insertion end 16 causedby over tightening the set screw 38 and reduces or eliminates thepossibility that the set screw 38 will vibrate loose from the tightenedposition.

Referring back to FIG. 3, the nominal length 39 of the bell portion 20(i.e., the distance from the edge of the length of conduit on thereceiving end to the transition run 22) should measure greater than 3.0inches, and preferably measures between 3.5 and 4.0 inches to providethe most efficient mechanical fit. Increasing the length 39 of the bellportion 20 results in an increase in the amount of surface area of thebell portion 20 in contact with the insertion end 16. In turn, anincrease in surface area contact provides an improved mechanicalconnection between the insertion end 16 and the bell portion 20.

In the preferred embodiment, the bell portion 20 is manufactured using aconduit end expander 44. The end expander 44 is inserted into anunexpanded conduit length 45 (FIG. 5A) until a bell portion 20 having adesired length is formed (FIG. 5B). Preferably, the end expander 44 issized and configured to form a bell portion 20 having a nominal lengthof at least three inches. After the bell expansion step, the conduit isloaded or transferred to a multitask station 46. At the multi-taskstation 46, the conduit is fixedly held while the multi-task station 46performs the following tasks on the conduit: forming the apertures 30and the raised crests 34 in bell portion 20; placing and clinching therivets 32 into the apertures 30; and placing and tightening the setscrews 38 into the rivets 32. Preferably, the conduit is fixedly held infront of the multi-task station 46 by electromagnets or other suitablemethods.

As illustrated in FIG. 6, the multi-task station 46 is preferably arotating table 48. With such a construction, the three aforementionedtasks can be performed on the conduit without having to move orreposition the conduit. For instance, in Step 1, a punch machine 50located on the rotating table 48 is positioned in front of the conduit.The punch machine 50 forms or punches the apertures 30 in the bellportion 20 and forms the raised crests 34 in the bell portion. In Step2, the rotating table 48 rotates 120° until a rivet machine 52 ispositioned in front of the conduit. The rivet machine 52 places andclinches the rivets 32 into the apertures 30. In Step 3, the rotatingtable 48 rotates 120° until a set screw machine 54 is positioned infront of the conduit. The set screw machine 54 places the set screws 38into the rivets 32 and tightens the set screws 38 such that the setscrews 38 will not vibrate loose during the shipping of the conduit.After the above tasks are performed on the conduit, the conduit istransferred to a finishing station where the conduit is prepared forshipping to end-users in the field.

In another embodiment, the multi-task station 46 may also be configuredto perform the bell expansion step. With such a construction, all fouraforementioned tasks can be performed on the conduit without having tomove or reposition the conduit. For instance, as illustrated in FIG. 7,in Step 1, end expander machine 56 located on the rotating table 48 ispositioned in front of the conduit. The end expander machine 56 forms abell portion 20 having a desired length and shape in the conduit. InStep 2, the rotating table 48 rotates 90° until the punch machine 50 ispositioned in front of the conduit. The punch machine 50 forms orpunches the apertures 30 in the bell portion 20 and forms the raisedcrests 34 in the bell portion. In Step 3, the rotating table 48 rotates90° until the rivet machine 52 is positioned in front of the conduit.The rivet machine 52 places and clinches the rivets 32 into theapertures 30. In Step 4, the rotating table 48 rotates 90° until the setscrew machine 54 is positioned in front of the conduit. The set screwmachine 54 places the set screws 38 into the rivets 32 and tightens theset screws 38 such that the set screws 38 will not vibrate loose duringthe shipping of the conduit. After the above tasks are performed on theconduit, the conduit is transferred to a finishing station where theconduit is prepared for shipping to end-users in the field.

In the foregoing specification, the present invention has been describedwith reference to specific exemplary embodiments thereof. It will beapparent to those skilled in the art, that a person understanding thisinvention may conceive of changes or other embodiments or variations,which utilize the principles of this invention without departing fromthe broader spirit and scope of the invention. The specification anddrawings are, therefore, to be regarded in an illustrative rather thanrestrictive sense.

1. A conduit coupling assembly for connecting multiple lengths ofconduit for containing electrical cable comprising, in combination: afirst length of conduit including an insertion end with an outsidediameter defining an outer surface; a second length of conduit includinga bell portion with an inner diameter defining an inner surface, thebell portion shaped and configured to receive the insertion end of thefirst length of conduit, the bell portion including at least a first andsecond aperture formed therethrough; a rivet fixedly secured in eachaperture, the rivet having internal threads for receiving a threaded setscrew, each set screw having a head with a bottom contacting surface;whereby the outside surface of the rivet contacts the bottom contactingsurface of the head of the set screw to provide frictional engagementbetween the rivet and the set screw when the set screw is in a tightenedposition, effective to achieve tightening with ¼ to 1½ turns, whereineach aperture is located on a raised boss so that when the rivets aredisposed within the apertures, an inside surface of the rivets sitssubstantially flush with the inner surface of the bell portion, whereinthe apertures are aligned on the bell portion in radial alignment or inlongitudinal alignment, wherein the bell portion includes a first and asecond end, the first end defined by an end of a receiving end and thesecond end defined by a transition run, whereby the distance between thefirst end and the second end is greater than 3 inches, wherein each setscrew has a double lead thread or a triple lead thread, wherein each setscrew includes a thread profile measuring between 4 and 12 threads perinch and a length measuring less than 0.5625 inches, and wherein thedifference between the inner diameter of the bell portion and theoutside diameter of the insertion end is less than 0.060 inches toprovide an improved mechanical fit between the lengths of conduit whenthe insertion end is positioned in the bell portion.